Tanning of hides and skins



May 17, 1938. M. M. MERRrr'r TANNING OF HIDES vAND SKINS Filed April 16, 193e AME/V70@ Patented May 17, 1938 UNITED. STATES' TANNING F HIDES AND SKINS Matthew M; Merritt, Middleum, Mass... signor to The Tanning Process Company, Boston, Mass., a corporation of Massachusetts Application April 16,1936, serial No. 74.732

9 Claims.

This invention' relates to the art of treating hides and. skins in the manufacture of leather therefrom. While the invention is exemplified by q reference to the chrome tanning of skins, it is to be understood vthat the invention and various characteristics thereof `may have other applications and uses.

It is an object of the invention to expedite the tanning of hides and skins and at the same time to 10 secure increased uniformity in the quality of the product.

To 4these ends and in accordance with an important characteristic of the invention, hides or skins are subjected to treatment at high tempera- 16 tures to expedite the action of tanning materials takes place. to secure a Vline even grain withouty any wrinkles therein and, particularly in the case of light leathers, to secure extended area beyond .0 anything commonly known in the industry. Following the slicking-out operation, preferably on a smooth-surfaced portable work support, the latter with the skin slicked out thereon' is introduced into a heat chamber wherein the air tem- 3'5 perature is maintained Vat about 240 F., the skin being subjected to this heated airfor a short period of time, which maybe about 8 minutes. It is to be understood that the skin never reaches a temperature of 240 F. in the time specified, 40 since evaporation of water from' the skin is effective to maintain a much lowervtemperature in the skin while in said heat chamber. It ls probable that the temperature of the lskin does not exceed 150 F. The treatment in the heat chamber oper- 40 ates to secure uniformity` in the distribution of the tanning material andby accelerating chemical action to complete the'tanning of the skins in the shortv period mentioned; Hence these skins will maintain their extended area and will present '50 an unusually :une grain 'surface due to uniform tanning and to fact that all wrinkles were smoothed out int e substantialsetttng of the hide or skin substance could take" place".y Itv follows that both hides and' sa skins will be nf ully-tanned in an extraordinarily slickingfoperation before any short `time and will present a grain surface of unusual quality. Furthermore, in the. case of skins the area obtained will be from 10% to 15% greater than that commonly obtained b y ordinary tion of the reducing liquor without any substantial setting of the hide or skin substance before the hide or skin is slicked out in extended condition. By treating the skins in relatively small batches and passing them successively through the reducing liquor, it is possible, to readily secure a uniformity in the treatment which is accomplished fortuitously, if at all, by drumming skins in mass in drums, as commonly practised in tanneries.

Following the ,heat chamber treatment described in a preceding paragraph, the skins are promptly stripped from their portable Work supports and immersed in a tank of running Vwater at a temperature of aboutl50 F., the purpose being to wash out excess tanning material without reducing the temperature of the skins which may then be passed promptly along for other operations, as for instance, coloring and fatliquoring, 'although if desired a washing drum may be utilized prior tointroduction of the skins into the coloring and fatliquoring drum. 'I'he skins'are now ready to be again slicked. out on boards or other portable work supports and introduced into a drying apparatus of suitable construction.

These and other important characteristics of the invention will now be described in detail in the specification and then-pointed outmore particularlyin the appended claims.

In the drawing there is illustrated various machines and apparatuses which may be utilized in practising the tanning of hides or skins in accordance with this invention. v

In the illustrated assembly of machines and apparatuses, which are arranged in an ordercorresponding to the sequence of operations which may be followed in the tanning of skins by the twobath chrome process, there are provided at A two drums, each of a size to treat three dozen sheepskins with the first-bath' chrome preparation, by which a 4chrome tanning material may be drummed into the skins in about twenty minutes. Preferably, vone of the drums will be utilized in drumming the chrome preparation into a charge of sheepskina-for instance, and then the second drum will be used for a similar purpose while the skins from the rst drum are being transferred to a tank B. It is to be understood thai/the skins thus treated may, without detriment, remain in the tank B for some time andy be progressively transferred to reducing drums C, since the rst bath chrome preparation is preferably of such composition that little or no actual tanning of the smns takes place. It is only after the skins enter the reducing bath in the drums C that the chrome material commences to be deposited in and on the fibers of the hide or skin. Hence the skins are transferred from the tank B to the reducing drums C, preferably a few at a time. The ideal way would be to have the skins pass one at a time through a reducing solution in a tank or in a drum such as that shown at C, each skin remaining in the drum for such a time as to fall short of being completely penetrated throughout by the reducing solution. In practice each skin is in e. drum C only about three minutes so that it has barely been penetrated by the reducing agent and hence has not had time to become set as it would 'be if it were thoroughly tanned. In this connection it is to be noted that the action of the reducing agent is not instantaneous in causing the chrome material to be set on the hide or skin liber. As a matter of fact, in tanneriesy it is common practice to drum skins in the reduc- Vif each skin in turn be removed after about three minutes drumming in the reducing solution, and placed upon a board or other portable work support d shown in the stack at D, it may be readily vslicked out on such board so as to obtain an extendedvarea much greater than is possible by methods commonly practised in tanneries. It is to beunderstood that the lskins may remain for a longer timeJ in the hypo solution, the only disadvantage being that they will not slick out so readily or to the same extent. .From the stack of boards at D, the skin roughly spread out on its board d. will be passed to a slicking machine E of a type such as that shown in United States Letters Patent No. 2,088,578, granted August 3, 1937,

on an application flled in the names of Connor and Merritt. Alternatively, the slicking operation may be performed by hand slickers. From the slicking machine E the skin, together with its assembled board, is passed into a heat chamber F wherein air is circulated at a temperature of about 240 F. Air in the chamber is changed to ensure evaporation from `the hides or skins therein. 'I'he boardsld are carried into the chamberF by conveyors f, f running at a rate such as to carry each board in turn through the chamber in about 8 minutes. This step in the treatment of the skins is particularly -important since the heat to which the skins are subjected in the chamber expedites to a marked.- degree the fixation of the tanning materialand; perforce, the completionof the tanning operation.`V In other "words, in the travel of the skins 'through this chamber, and in about 8 minutes time, the tanning material has become uniformly distributed.

,throughout the hide or skin substance and has become so iixed in relation to the iibers'that the smooth grain surface provided by the slicking operation is maintained through all subsequent operations. For instance, the grain surface will not become wrinkled during drumming of the skin in such subsequent operations ascoloring and fatliquoring. Furthermore,'the extended area obtained by the slicking machineat E is also maintained during subsequent operations due to the fact that the chrome tanning material has become set in'and upon the hide substance.

Promptly after th-e skins appear at the discharge end of the chamber F, they are removed from the boards, this being easily accomplished since they were not attached to the boards' by any of the means usually employed for that purpose, the slicking of the skin out upon its supporting board being sumclent to maintain it upon the vertically positioned board during its travel to and through the chamber F. Hence, the skin may be lifted or stripped from the board with little eil'ort and be deposited in a hot water tank at G, while the board is placed upon the stack at I. The skins are placed in tank G to undergo a certain amount of washing and to be kept at a suitable temperature for the next operations, namely, the coloring and fatliquoring operations. Preferably, water at about 150 F. is continuously running into and out of the tank G. When enough skins have accumulated in the tank G to provide a charge for one of the small'drums at H. one of said drums is charged with the skins and with warm water for a washing operation lasting about thirty minutes, after which the liquid isl drained and a coloring solution added and the drumming continued for another thirty minutes. Then a fatliquor at a suitable temperature is added and the drumming continued for another thirty minutes. In the meantime, other batches of skins have accumulated in the tank G and have been transferred to one of the other drums at H to be treated as outlined above.

Skins from each drum H in turn are transferred, one at a time, to boards d in the stack I to be transferred promptly to a slicking machine at J. From the slicking machine J, the skins upon their boards are passed in the direction of the arrow to a tacking table at K where a suilicient number of light staples are inserted through marginal portions of the skins to hold them in position while they are drying on the boards. Subsequently the 'skins upon their boards are transferred to a drierI at L, which may be of any well-known type designed for the treatment of skins upon boards, but is preferably of the type of drier shown in United States Letters Patent No; 2,071,296, granted Feb. 16, A1937, on an applicationv led in the names of Connor and Merritt.

While, as described in the foregoing paragraphs, tanning material is. applied to hides and skins before they undergo a slicking-out operation, it is to be understood that these operations may be reversed. In other words, hides and skins may be slicked out upon a smooth work supporting surface and then. have tanning material applied thereto while the pieces oi' work remainv in slicked-out condition for a period sumcient to permit permeation of the hide or skin substance with the tanning material. Then the hide or skin, with or Without its work support, may be introduced into a heat chamber, like that shown at F, to expedite fixation of the tanning material uponthe fibers of the hide or skin.

However,it is preferable in practice to follow the 75 and skins to expedite xation vvof the tanning material upon the hide or skin substance is particularly applicable to the chrome tanning of hides and skins, it isa fact that excellent results have been obtained with skins treatedY with such widely different vegetable tanning materials as quebracho and sumac. The latter is mentioned particularly because of its tendency to cause shrinkage in the skins to which it is applied. The new .method of tanning, including the chamber treatment at air temperatures up to and including 240 F.. gives excellent results and serves to restrict very markedly the tendency to shrinkage of the sumac-tanned skins, due in part no doubt, to the fact that they are heat treated while slicked out on portable work supports. In general, hides and skins will receive tanning treatment for longer periods of time when vegetable tanning materials are used than in the case of mineral tanning substances since vegetable tanning materials penetrate more slowly. The fact that these vegetable tanned skins are not'injured in any way by the eight minutes treatment in the heated oven at 240 F. is of itself a proof that the skins do not rise to such a temperature, it being most probable that the temperature of the skin at the highest is not above ,150 F., due as stated to the effects of evaporation. Chrome tanned skins, on the other'hand. will stand much higher temperatures, so that the upper limit of the range of temperatures for chrome tanned skins within the chamber F may be substantially above 240 F. The heat .treatment while the hides or skins are still moderately wet with the tanning liquor secures uniform distribution of the tanning material throughout the hide or skin.

While the machines and apparatuses shown in the drawing may conveniently be used to practise the method which forms the subject-matter of this application, it is to be understood that the method in its entirety' and various important steps thereof may be practised by other means. For instance, while it is desirable that small drums such as those shown at A be used in the first-bath drumming of the skins. this is not essential since the skins from the first bath are not tanned and hence they may be treated in quantity in large drums and kept vfor a number of hours without deleterious effect. In other words, there is no danger of them shrinking or becoming set in a semi-tanned condition. Again, while it is preferable to utilize small drums of the type shown at C for the reducing solution, some other mechanism may be used in the operation, provided the skins are rpassed successively through the reducing solution at such a rate that each skin remains in the solution for a short time, about three or four minutes. A t the end of that time, each skin in turn is placed upon a board d in the stack D and is passed immediately to a slicking machine such as that shown at E. If desired, the'skins, of course, may be slicked out by hand and then the slicked-out skin and board placed in the conveyor mechanism f, f' of the oven F. Alternatively, hides or skins may be put out without the use of boards, in which case they may be suspended from-slats or rods in the heat chamber. When the skins come from f the chamber F, they are preferably placed in a hot water tank G to maintain them at a temperature suitable for such succeeding operations as coloring and fatliquoring. From this .point on any well-known mechanism may-be used for finishing of the skins.

Having fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. That improvement in methods of tanning hides and skins which comprises treating hides or skins with a tanning solution for a period of time just suiiicient to secure substantially complete penetration of the hide or skin substance by the tanning material, forthwith slicking out the hides or skins, and promptly introducing the `hides or skins for a short time into a chamber with the air therein at a temperature of about 240 F. to complete the tanning of the 'hides'` or skins in extended 'smoothed-out condition.

' 2. That improvement in methods of tanning hides and skins which comprises treating hides or skins with a tanning solution for a period Aof time just suillcient to secure substantially complete penetration of the hide or skin substance by the tanning material, forthwith slicking out the hides or skins upon portable work supports, and

promptly introducing the hides or skins on their l portable work supports into a chamber with the air therein at high temperatures of the order of 200 F. and over where the hides or skins are left for a period of about eight minutes to complete the tanning of the hides or skins in extended smoothed-out condition.

3. That'improvement in methods of tanning hides and skins which comprises slicking out the hide or skin to provide a smooth grain surface and an extended area, applying tanning material to the slicked-out hide 'vor skin in a quantity sui!- iicient to tan said hide or skin, the tanning material being allowed to act upon the hide or skin for a time just suiiicient to secure substantially complete penetration thereof by the tanning material, and then promptly subjecting the hide or skin in its slicked-out condition to heat treatment for a short time in air at a temperature of about 240 F. to effect tanning thereof in an extended, smoothed-out condition.

4. That improvement in methods of tanning hides and skins which comprises applying tanning material to a hide or skin in a quantity sufficient to tan said hide or skin, the tanning material being allowed to act upon the hide or skin for a time barely sumcient to secure substantially complete penetration thereof by the tanning ma terial without substantial fixation of the tanning material on the hide or skin bers, slicking out the hide or skin to provide a moothgrain surface and an extended area, and en promptly placing the hide or skin in itsslicked-out conditionfor a short time in a chamber having air circulating therein at a temperature of about 240 F. to effect tanning thereof in an extended, smoothedout condition.

5. That improvement in methods of tanning hides and skins which comprises treating hides or skins with a tanning solution for a period of time just suiilcient to secure substantially complete penetration of the hideA or skin substance by the ltanning materiall then promptly slicking out the minutes to complete the ,tanning of the hides or skins in extended smoothed-out condition, stripping the hides or skins from the work supports, and promptly introducing them into Water at a temperature of about 150 vF. wherein they undergo a washing operation and in which they are maintained'at a temperature suitable for the subsequent operations such as coloring and fatliquoring.

6. That improvement in methods of chrome tanning hides and skins which comprises treating the hides or skins with a chrome tanning preparation which in itself is substantially non-tanning to secure complete permeation of the hides or Skins with said tanning preparation, subjecting these hides or skins to treatment by a reducing solution for a brief period of time insufiicient to effect setting of the chro'me material upon the hide or skin substance, promptly slicking out the hide or skin to secure a smooth grain surface and extended area, and then subjecting the hide or skin in its slicked-out condition to heat treatment by air circulating at a temperature of about 240 F. to expedite setting of the chrome material upon the hide or skin substance.

7. That improvement in methodsj of chrome tanning hides and skins which comprises drumming the hides or skins'with a chrome tanning preparation which in itself is substantially nontanning to secure complete permeation of the hides or skins with said tanning preparation, subsequently subjecting these hides or skins in succession to treatment by a reducing solution for a brief period of time insuicient to effect xation of the crome material upon the hide or skin substance, promptly slicking out the hide or skin to secure a smooth grain surface and extended area, and then heat treating the hide -or skin at a temperature of 150 F. and over to expedite xation of the chrome material upon the hide or skin substance whereby the hide or skin is completely tanned in smoothed-out extended v condition.

8. That improvement in methods of tanning hides and skins with vegetable tanning extracts in solution which comprises heat treating'l the hides or skins for a short time ln -a chamber having air circulating at a temperature of about 240 F. after they have been slicked out and have had tanning material freshly applied thereto,

whereby tanning of the hides or skins is rapidly MA'I'I'HEW M. MERRITT. 

